The present invention relates to a semiconductor device and a method of manufacturing the same and, more particularly, to a semiconductor device a part of which is formed on a substrate of a first semiconductor by using a second semiconductor material having an energy gap larger than that of the first semiconductor, and a method of manufacturing the same.
A conventional semiconductor device a part of which is formed on a substrate of a first semiconductor by using a second semiconductor material having an energy gap larger than that of the first semiconductor and a method of manufacturing the same have the following drawbacks.
(1) Since the conventional semiconductor device has a structure wherein a second semiconductor is exposed on a surface of the device, wiring operations and the like must be performed for the first and second semiconductors, respectively. For example, in a silicon heterojunction bipolar transistor in which a base and a collector are formed on a silicon substrate, and an emitter of a compound semiconductor having an energy gap larger than that of silicon is formed thereon, since the material of the emitter is different from that of the base and collector, a wiring material and a wiring method suitable for each element must be applied. Therefore, the manufacturing steps such as wiring are complicated.
(2) Since the second semiconductor is exposed on the surface during manufacturing, impurity contamination is undesirably caused by the second semiconductor such as a material for the emitter, and hence a first semiconductor (e.g., silicon) process line cannot be used after the second semiconductor is formed.
(3) Since an electron barrier is formed on the interface between the first and second semiconductors, a contact resistance is increased and the characteristics of the device are undesirably degraded. In order to eliminate the above drawbacks, for example, in the silicon heterojunction bipolar transistor, in order to form an ohmic contact with an emitter formed using a material such as a compound semiconductor having a large energy gap, an impurity is heavily doped in a contact portion with an emitter electrode material by ion implantation, or a wiring material for the emitter must be varied from that for the base and collector.
According to the above method, however, since the activation ratio of the impurity doped in the emitter material having a large energy gap is limited, a contact resistance is not sufficiently decreased.